Method capable of accurately controlling electron energy of electron gun

Abstract

The invention discloses a method capable of accurately controlling electron energy of an electron gun, and the method comprises the following steps: S1, in the working process of the electron gun, heating a filament of the electron gun, not adding an ionization energy electric field, not emitting electrons, and cutting off a filament heating power supply until the heating is completed, and obtaining electrons in an activated state at the moment; s2, after the S1 process, an ionization energy electric field is applied to the filament and the ionization chamber, and electrons in an activated state are pulled out; s3, alternately performing S1 and S2 by using a pulse duty ratio scheme; the multiple electron guns are arranged in the vertical direction of the ionization chamber, it can be guaranteed that the electron beams conduct ionization on the sample continuously without losing the sample, and in addition, the ionization energy band ionization method or the electron energy band scanning ionization method is achieved by combining ion deflection and the multiple ionization energy electron guns which are connected in series.

Description

Technical Field

[0001] The invention relates to the technical field of ion sources, in particular to a method for accurately controlling electron energy of an electron gun. Background Art

[0002] The conventional electron impact ion source (EI) is a tungsten filament or tungsten alloy filament heated by a power supply, and the power supply is superimposed on a negative voltage, such as -60V. Then the filament is close to the slit of the ionization chamber, and the ionization chamber is powered, such as +10V, so that the heated activated electrons will be pulled out from the filament surface by the electric field force applied to the filament and the ionization chamber, and the electrons will be accelerated into the ionization chamber under the action of the above electric field, and an energy-controllable electron flow will be obtained, which can be used in electron guns such as mass spectrometry or scanning electron microscopes. Taking mass spectrometry as an example, the conventional method is to obtain 70ev electron energy (because electrons at this energy can produce a high ion quantity signal that is stable and repetitive in the sample), and two filaments will be installed symmetrically on both sides of the ionization chamber as a backup. A concave electrode is added to the filament to enable the electrons to be better focused into the ionization chamber, and in order to allow the electrons to have more collision interfaces with the sample in the ionization chamber, a magnetic field will be arranged on the ionization path to make the electrons spiral forward.

[0003] However, the different positions where electrons come out of the filament will have potential differences due to the voltage used to heat the filament, causing large differences in the energy of the electron beam coming out. This difference has a more prominent impact, especially as some recent scientific research requires the use of low electron energy to obtain electron beams.

[0004] Therefore, the present invention provides an electron gun with precisely controlled electron energy. When the filament is heated, no electric field for pulling electrons is provided, and when an electron beam is needed, the filament is not heated, that is, there is no voltage difference on the filament. Since the temperature of the heated filament is a physical macroscopic phenomenon and will not change instantaneously, a pulse duty cycle scheme is used to alternately control heating and pulling electron beams, which can ensure that the filament has enough thermal energy to emit electrons and also ensure that the potential of the filament is the same when electrons are emitted, so that the electron gun emits electrons with precisely controlled energy. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention aims to provide a method for accurately controlling the electron energy of an electron gun.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions: The present invention provides a method for accurately controlling the electron energy of an electron gun, comprising the following method: S1, during the operation of the electron gun, the filament of the electron gun is first heated without applying an ionizing energy field and emitting electrons until the heating is completed and the filament heating power supply is disconnected, at which time activated electrons are obtained; S2, after the electron gun filament is heated and the heating power is disconnected, an ionizing energy field is applied to the filament and the ionization chamber to emit electrons and pull out the activated electrons; S3, alternately performs S1 and S2 using a pulse duty cycle scheme to control the power supply of the electron gun and obtain high-precision electron energy, that is, obtain electrons with high-precision energy; this is to control the power supply of the electron gun to both heat the filament and provide an ionization energy field, that is, to obtain excited electrons during heating, and to pull the excited electrons out of the filament when the ionization energy field is increased to obtain high-precision electron energy.

[0007] Preferably, when there is a small difference in the accuracy of the acquired electron energy, a deflection electric field is first used to make the electrons take different paths according to the energy difference, and then a deflection field of the same size is applied in the reverse direction so that the energy electrons are deflected back to the original state through a fixed path. At this time, electrons with fixed energy will pass through a fixed path, and then the slits are used to restrict the passage of electrons that are not on the corresponding path, that is, those with energy differences. That is, only electrons with set accuracy energy are deflected by the left electric field and can pass through the slits. Then the reverse right electric field is used to recover the energy in the vertical direction increased by the deflection and convert it into electric potential energy, so that electrons with higher accuracy energy can be obtained.

[0008] Preferably, several electron guns are arranged in the vertical direction of the ionization chamber and work in time-sharing mode to ensure that high-precision energy electrons are always present in the ionization chamber to ionize the sample.

[0009] Preferably, several electron gun groups with different energies are arranged along the path through which the ionized sample passes, and the electron energy forms several electron gun areas from low to high, that is, several electron energy ionization zones. When the last electron gun with lower energy completes the ionization of the sample, the ions are deflected by the deflection electric field, and the remaining samples that cannot be ionized by the low electron energy are ionized by the electrons with higher ionization energy in the next electron gun area with higher ionization energy when passing through the area. Thus, the information of sample ions ionized only by electrons with target ionization energy can be obtained, and this group of ionization energies can be changed synchronously to realize the method of energy band scanning ionization.

[0010] The beneficial effects of the present invention are: the method of the present invention can accurately control the electron energy of the electron gun, (1) The heated filament of the electron gun is brought into an activated state of electrons, and an electric field is applied to the filament and the ionization chamber to pull out the activated electrons. At the same time, the potential difference of this electric field is used to obtain the energy of the electrons entering the ionization chamber. These two processes are separated and performed alternately using a pulse duty cycle scheme. This avoids the voltage applied to the filament causing a difference in potential at different positions on the filament, resulting in the energy of the emitted electrons being within this potential difference range. After eliminating this range of electron energy caused by this difference, highly precisely controlled electron energy is obtained. (2) Apply a deflection electric field and prepare a slit on the path through which the electron energy passes, through which only electrons with corresponding electron energy can pass. This can more accurately control the electron energy and ensure that the electron energy is better than 100 meV. (3) Arranging multiple electron guns in the vertical direction of the ionization chamber can ensure that the electron beam ionizes the sample continuously and does not miss the ionization of the sample; (4) Electron gun groups with different energy levels are arranged on the sample path, and the ions ionized by the previous lower energy electron gun are deflected by a deflection ion gate structure, and then the higher energy electron gun group is used to ionize the sample that cannot be ionized by the previous electron gun, so as to obtain the ion information of the target ionization energy of the sample. That is, the present invention is a method of realizing ionization energy band ionization or a method of electron energy band scanning ionization by combining ion deflection and the above-mentioned multiple ionization energy electron guns in series. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0012] Figure 1 A working principle diagram of a method for accurately controlling electron energy of an electron gun provided by an embodiment of the present invention, wherein the reference numerals represent an ionization power supply 1, an ionization chamber power supply 2, a filament power switch 3, and a reverse electron voltage 4 respectively; Figure 2 The electron beam with precise energy obtained by the embodiment of the present invention, wherein the curve is the trajectory path of electrons with a certain energy difference passing through the lateral acceleration and deceleration of the vertical electron energy (vertically upward), the boxes A and B are the slits constraining the designed path, and the potential of the space on the right is the same as that of the space on the left, and only electrons with the set electron energy can pass smoothly; Figure 3 For the detection sequence of the time-of-flight mass spectrometer as an example scheme, the analysis trigger function of the time-of-flight mass spectrometer is turned on during the ionization energy period to obtain mass spectrum information; Figure 4A schematic diagram of an ion deflection and multiple ionization energy electron guns connected in series according to an embodiment of the present invention, wherein the positive and negative deflection electric fields deviate from the ions ionized in the previous lower ionization energy band, and the reference numerals represent an ionization power supply 1, an ionization chamber power supply 2, a filament power switch 3, and a reverse electron voltage 4, respectively. DETAILED DESCRIPTION

[0013] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0014] Examples, such as Figure 1 to Figure 2 As shown, the present invention provides a method for accurately controlling the electron energy of an electron gun, including the following method: S1, during the operation of the electron gun, only the filament of the electron gun is heated without applying an ionizing energy field and emitting electrons, until the heating is completed and the filament heating power supply is disconnected, at which time activated electrons are obtained; S2, after the filament of the electron gun is heated in the ionization chamber and the heating power is disconnected, an ionization energy field is applied to the filament and the ionization chamber to emit electrons and pull out the activated electrons; S3, alternately performs S1 and S2 using a pulse duty cycle scheme to control the power supply of the electron gun and obtain high-precision electron energy, that is, obtain electrons with high-precision energy; this is to control the power supply of the electron gun to both heat the filament and provide an ionization energy field, that is, to obtain excited electrons during heating, and to pull the excited electrons out of the filament when the ionization energy field is increased to obtain high-precision electron energy.

[0015] Further, such as Figure 2 As shown, when the accuracy of the obtained electron energy is still not enough (that is, a small difference occurs), a deflection electric field is first used to make the electrons take different paths according to the energy difference, and then a deflection field of the same magnitude is applied in the reverse direction, so that the electrons with this energy are deflected back to the original state through a fixed path. At this time, electrons with fixed energy will pass through a fixed path, and then the slits are used to restrict the passage of electrons that are not on the corresponding path, that is, those with energy differences. That is, only electrons with set accuracy energy can pass through the slits after being deflected by the left electric field. Then the reverse right electric field is used to recover the energy in the vertical direction increased by the deflection and convert it into electric potential energy, so that electrons with higher accuracy energy can be obtained.

[0016] Further, such as Figure 1 As shown, several electron guns are arranged vertically in the ionization chamber and work in time-sharing mode to ensure that there are high-precision energy electrons in the ionization chamber at any time to ionize the sample.

[0017] Further, such as Figure 4 As shown, several electron gun groups with different energies are arranged along the path through which the ionized sample passes, and the electron energy forms several electron gun areas from low to high, i.e., several electron energy ionization areas. When the last electron gun with lower energy completes the ionization of the sample, the ions are deflected by the deflection electric field, and the remaining samples that cannot be ionized by the low electron energy are ionized by the electrons with higher ionization energy in the next electron gun area with higher ionization energy when passing through the area. Thus, the information of sample ions ionized only by the electrons with the target ionization energy can be obtained, and this group of ionization energies can be changed synchronously to realize the method of energy band scanning ionization.

[0018] Working principle: exist Figure 1 middle, (1) The filament power switch is mainly used to control whether the filament is heated or not. At the same time, when the filament is not heated, the filament is cut to the ionization energy voltage, that is, to control the voltage difference between the ionization chamber and the filament, so that the filament has enough electric field to the nearest electrode to generate electrons. At the same time, this voltage difference is also the potential energy of the potential difference obtained by the electrons from the filament into the ionization chamber; (2) When the filament is heated, the switch is turned on, and at the same time, the ionization chamber potential is switched at the other end of the filament, so that there is no negative pressure difference between the filament and the ionization chamber during heating, ensuring that basically no electrons are emitted; for example, when the filament is heated and the ionization chamber is at negative 5V, one end of the filament is at negative 5V and the other end is at positive 7V. In this way, there is no negative pressure difference between the filament and the ionization chamber, and the electron potential on the filament is higher than that of the ionization chamber, so no electrons are generated. When the EI needs to emit electrons, the ionization chamber is adjusted to positive 10V, and the other end of the filament used for heating is disconnected and positive 7V is connected. The filament will be pulled to the same potential by the negative 5V end, so that electrons with an electron energy of 15eV can be obtained in the ionization chamber; (3) Use the pulse duty cycle scheme to control the switching of the filament between the heating process and the electron emission process; (4) Although the potential of the filament where the electrons are generated has been controlled, the generated electrons may still have work function, that is, the generated electrons still have energy when they escape from the filament. In this case, the generated electrons can be detected by a method similar to mass spectrometry (such as Figure 2 As shown in the figure), electrons under electric field control are selected through a fixed path, and only the electrons passing through this path are used for subsequent ion generation and other functions, that is, when the energy electrons are deflected by the left and right electric fields and pass through the slits, the energy added by the left and right electric fields is corrected back to the original electron energy by the reverse left and right electric fields, or other methods such as mass spectrometry can be used to constrain the electrons in a very small range of electron energy, specifically: 1. The generated electron beam is analyzed in vertical and horizontal directions after passing through the deflection electric field. The vertical direction is the direction of the required ion energy and will not be affected by the vertical electric field. 2 Such as Figure 2 As shown, when an electric field is applied in the horizontal direction, electron energy that is not required by the design will be submerged in the electrode because the applied horizontal electric field cannot accurately pass through the slit, while the required electron energy passes through the path with the channel at the speed in the vertical direction; that is, ions that do not meet the vertical speed will not pass through the designed path and will be submerged in the electrode, and the energy of electrons that meet the requirements in the horizontal direction will be recovered by the electric field, and the electrons that finally go out are only the electrons in the vertical direction that meet the required energy.

[0019] The method for accurately controlling the electron energy of an electron gun in the present invention is as follows: (1) by controlling the heating of the filament of the electron gun and providing electron energy in a time-sharing manner, the emitted electron energy is not affected by the pressure difference of the heating filament; (2) by applying a deflection electric field, a slit or other scheme is used to select electrons with fixed electron energy to pass through the slit and enter the ionization chamber, thereby obtaining electron energy with higher precision, and being free from the constraints of time-sharing control, that is, the electron energy that is not time-sharing controlled can also be screened for accurate energy through this scheme; (3) by symmetrically arranging multiple electron guns and working in time, an electron flow that works continuously in time is obtained; (4) by arranging multiple electron energy ionization zones from low to high, first ionizing molecules with low ionization energy and deflecting them, the deflected sample ions can be directly detected, and then the unionized samples are ionized by electrons with higher ionization energy, and energy scanning can be performed.

[0020] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for accurately controlling the electron energy of an electron gun, characterized in that: The methods included are as follows: S1, during the operation of the electron gun, the filament of the electron gun is first heated without applying an ionizing energy field and emitting electrons until the heating is completed and the filament heating power supply is disconnected, at which time activated electrons are obtained; S2, after the filament of the electron gun is heated and the heating power is disconnected, an ionizing energy field is applied to the filament and the ionization chamber to emit electrons and pull out the activated electrons; S3, alternately performing S1 and S2 using a pulse duty ratio scheme to control the power supply of the electron gun and obtain high-precision electron energy, that is, obtaining electrons with high-precision energy.

2. A method for accurately controlling electron energy of an electron gun as claimed in claim 1, characterized in that: When there is a small difference in the accuracy of the obtained electron energy, a deflection electric field is first used to make the electrons take different paths according to the energy difference, and then a deflection field of the same size is applied in the reverse direction to deflect the electrons with this energy back to their original state through a fixed path. At this time, electrons with fixed energy will pass through a fixed path, and then the slits are used to restrict the passage of electrons that are not on the corresponding path, that is, those with energy differences. That is, only electrons with set energy accuracy can pass through the slits after being deflected by the left electric field. Then the reverse right electric field is used to recover the energy in the vertical direction increased by the deflection and convert it into electric potential energy, so that electrons with higher energy accuracy can be obtained.

3. A method for accurately controlling the electron energy of an electron gun as claimed in claim 1 or claim 2, characterized in that: Several electron guns are arranged vertically in the ionization chamber and work in time-sharing mode to ensure that there are high-precision energy electrons in the ionization chamber to ionize the sample at any time.

4. A method for accurately controlling electron energy of an electron gun as claimed in claim 3, characterized in that: Several electron gun groups with different energies are arranged along the path through which the ionized sample passes, and the electron energy forms several electron gun areas from low to high, i.e., several electron energy ionization zones. When the last electron gun with lower energy completes the ionization of the sample, the ions are deflected by the deflection electric field, and the remaining samples that cannot be ionized by the low electron energy are ionized by the electrons with higher ionization energy in the next electron gun area with higher ionization energy when passing through the area. Thus, the information of sample ions ionized only by electrons with target ionization energy can be obtained, and this group of ionization energies can be changed synchronously to realize the method of energy band scanning ionization.

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